Microwave Power Loss Research Articles

Simulation and Measurement of an Interaction Structure With Distributed Radiation Coupling Circuit for a High-Power Ku-Band Gyro-TWT

Design and measurement of a distributed radiation coupling (DRC) circuit for the Ku -band TE11-mode gyrotron traveling wave tube (gyro-TWT) amplifier are presented. Different from the dielectric-loaded (DL) waveguide, the proposed DRC circuit can suppress the parasitic modes by achieving sufficient radiation coupling losses. It has the merit of lowering the microwave power loss density, which can improve the tube stability and average power-handling capability. Based on this proposed DRC circuit, a Ku -band TE11-mode gyro-TWT was designed and the particle-in-cell (PIC) simulation shows it can obtain a saturated output power of over 150 kW from 15.3 to 17.2 GHz for an electron beam with a velocity spread of 4.35%. As a comparison, the maximum average microwave power loss density is only 20% of the DL circuit under the same operating parameters. For verification, a DRC circuit was manufactured and cold tested. The maximum deviation between the measured results and our analysis is within 10%.

Parallel-pumped nonlinear loss effects for polycrystalline yttrium iron garnet in the high-power microwave environment

In this study, the parallel-pumped nonlinear (NL) loss effects of polycrystalline Yttrium Iron Garnet (YIG) material caused by the high-power microwave (HPM) were explored for the first time. In terms of the coupling process of spin waves and electromagnetic waves, the improved ferrite NL theory encompassing the input microwave waveform parameters (pulse duration and power) was developed. The theoretical and experimental results indicated that the critical threshold power of the NL effect is approximately inversely proportional to incident microwave pulse with a duration below 80 ns, demonstrating the features of the energy threshold. Furthermore, the theoretical calculation and the high-power measurements show that the polycrystalline YIG sample exhibits a relatively stable microwave power loss trend in the HPM environment with input power of 160 W–400 W. The influence of the external magnetic bias field on the YIG nonlinear effects was also carried out for comparative analysis. This research not only expanded the NL loss theory of ferrite in the nanosecond-level microwave environment but also offered a potential limiting protection application against HPM electromagnetic environment threats.

High-performance microwave absorption heating honeycomb sandwich composite with electroless nickel-plated glass fiber

This paper presents a multi-functional nickel-plated glass fiber honeycomb sandwich composite (MNHSC), a heating element that uses microwave absorption mechanisms. To design the MNHSC, a nickel-plated glass fiber was prepared using the electroless plating method to modify the thermal and electrical properties. An MNHSC with a microwave absorption performance of −22 dB at 2.45 GHz was designed to maximize its performance as a heating element by employing a coupled design method of microwave absorption and power loss density. In microwave heating experiment, the MNHSC was heated up to 160.6 °C within 1700 s with a microwave power of 500 W, indicating a 0.50 °C/s temperature increase rate to 100 °C. In addition, a flatwise compressive test was conducted to check their feasibility in terms of structural integrity caused by thermal effect, the results of which indicated that the proposed MNHSC could offer a promising solution for multi-functional de-icing applications.

Dielectric properties of water relevant to microwave assisted thermal pasteurization and sterilization of packaged foods

Microwave assisted thermal sterilization and pasteurization systems, as emerging thermal processing technologies, use circulation water to reduce edge heating of the food packages in the microwave heating sections. Yet, the influence of the circulation water on microwave heating efficiency for food is unknown. This research studied the dielectric properties of purified water from a reverse osmosis unit and tap water over microwave frequencies of 150–2500 MHz at 23–120 °C and evaluated microwave loses in the circulation water. The values of the dielectric constant of purified and tap water decreased (P < 0.05) with increasing temperature and slightly decreased with increasing frequency. The value of the loss factor of purified water also decreased with temperature (P < 0.05) but increased with frequency. The trend was more complicated for the loss factor of tap water. The penetration depth of 915 MHz microwave power in purified water was 399 and 457 mm at 90 and 120 °C, respectively, it was reduced to 161 and 136 mm in tap water. The microwave power loss in the 18–30 mm deep purified water, depending on the thickness of the food packages, was 4–7%, compared to 11–20% in tap water. Thus, using purified circulation water in microwave assisted thermal sterilization (MATS) and pasteurization systems (MAPS) can significantly improve the efficiency of microwave heating of packaged foods. Industrial relevanceThe information from this research are highly relevant to industrial operations of microwave-assisted thermal sterilization and pasteurization systems of pre-packaged foods. The dielectric property data will contribute to the literature related to the physical properties of water in microwave heating.

A Bandpass Filter–Polarizer Based on a Dielectric Multilayer with Strip Conductor Gratings

A new design of a multilayer bandpass filter is proposed, in which each resonator consists of two identical dielectric layers with parallel strip conductor gratings on their outer surfaces and an orthogonal strip conductor grating between the layers. The filter designed on the basis of crossed gratings works simultaneously as a polarizer transparent in a specified frequency band if the electric field vector of a wave is parallel to the outer strip conductors but reflects waves with an orthogonal polarization. The data from a numerical electrodynamic analysis of a 3D model of the proposed device agree well with the results of the measurements performed on the fifth-order filter–polarizer prototype with a relative bandwidth of 14% and a central frequency of 13.4 GHz. The microwave power loss in the filter passband is ~1.2 dB under parallel polarization of the electromagnetic wave and more than 40 dB under orthogonal polarization.

Broadband W-band Rapid Frequency Sweep Considerations for Fourier Transform EPR.

A multi-arm W-band (94 GHz) electron paramagnetic resonance spectrometer that incorporates a loop-gap resonator with high bandwidth is described. A goal of the instrumental development is detection of free induction decay following rapid sweep of the microwave frequency across the spectrum of a nitroxide radical at physiological temperature, which is expected to lead to a capability for Fourier transform electron paramagnetic resonance. Progress toward this goal is a theme of the paper. Because of the low Q-value of the loop-gap resonator, it was found necessary to develop a new type of automatic frequency control, which is described in an appendix. Path-length equalization, which is accomplished at the intermediate frequency of 59 GHz, is analyzed. A directional coupler is favored for separation of incident and reflected power between the bridge and the loop-gap resonator. Microwave leakage of this coupler is analyzed. An oversize waveguide with hyperbolic-cosine tapers couples the bridge to the loop-gap resonator, which results in reduced microwave power and signal loss. Benchmark sensitivity data are provided. The most extensive application of the instrument to date has been the measurement of T1 values using pulse saturation recovery. An overview of that work is provided.

Effect of Sand Base Grade and Density of Moulding Sands with Sodium Silicate on Effectiveness of Absorbing Microwaves

Abstract In the paper, presented is a research on effectiveness of absorbing electromagnetic waves at frequency 2.45 GHz by unhardened moulding sands prepared of three kinds of high-silica base and a selected grade of sodium silicate. Measurements of power loss of microwave radiation (Pin) expressed by a total of absorbed power (Pabs), output power (Pout) and reflected power (Pref) were carried-out on a stand of semiautomatic microwave slot line. Values of microwave power loss in the rectangular waveguide filled with unhardened moulding sands served for determining effectiveness of microwave heating. Balance of microwave power loss is of technological and economical importance for manufacture of high-quality casting moulds and cores of various shapes and sizes. It was found that relative density influences parameters of power output and power reflected from samples of moulding sand placed in a waveguide. Absorption expressed by the parameter Pabs is not related to granularity of high-silica base: fine, medium and coarse. It was found that the semiautomatic microwave slot line supports evaluation of effectiveness of microwave absorption on the grounds of power loss measurements and enables statistic description of influence of relative density of the sandmix on penetration of electromagnetic waves in unhardened moulding sands.

Optimal design of a standing-wave accelerating tube with a high shunt impedance based on a genetic algorithm

In this paper, we present an optimal design based on a genetic algorithm for a compact standing-wave (SW) accelerating tube with an operating frequency of 2998MHz for industrial and medical applications. It consists of bi-periodic structures with a nose cone whose inter-cavity coupling is achieved through electric coupling rather than magnetic coupling. A mathematical model is established to optimize the arc at the cavity wall to reduce the microwave power loss and to optimize the nose cone to increase the electric field along the axis to achieve a high shunt impedance. The simulation results indicate that with the proper nose cone and arc, the shunt impedance of the cavity can be as high as 114MΩ/m. Afterward, we present the tuning of the tube using SUPERFISH and the calculation of the beam dynamics using ASTRA and Parmela. The total length of the optimal tube is only 30.175cm. Finally, a coupler is designed with a small-aperture coupling using CST MICROWAVE STUDIO.

Quantitative microwave‐induced thermoacoustic tomography

Microwave-induced thermoacoustic tomography (MI-TAT) is an imaging modality that exploits dielectric contrast while producing images with high ultrasound resolution. Existing reconstruction algorithms for MI-TAT are qualitative and can image only the distribution of the absorbed microwave energy or power loss density. Here the authors describe a method for quantitative MI-TAT and obtain the distribution of dielectric property which directly correlates with tissue structural and functional information. The authors implement the quantitative MI-TAT method based on the finite-element (FE) solution to the Helmholtz equation for electromagnetic field coupled with the thermoacoustic wave equation. Regularization techniques are also used in the FE-based reconstruction algorithm. Simulation results are obtained under various practical scenarios including different noise levels, different contrast levels between the heterogeneity and background region, and multiple targets with various sizes and shapes. The quantitative MI-TAT method described can provide accurate recovery of conductivity distribution in heterogeneous media and is insensitive to noise effect.

Investigation of the Failure Mechanism for an S-Band Pillbox Output Window Applied in High-Average-Power Klystrons

On the basis of the results of X-ray photoelectron spectroscopy, theoretical analyses, and numerical simulations, the failure mechanism of an S-band pillbox output window applied in a high-average-power klystron is discussed. The influence of the high-order cylindrical-guide modes on the microwave power loss, the direction of the power flow and the window disk cracking are investigated. The high-order cylindrical-guide TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode existing on the surface of the window ceramic disk may cause the carbon film deposition and excessive radio frequency losses on the disk and lead to the breakdown of the window.

Glow plasma trigger for electron cyclotron resonance ion sources

Electron cyclotron resonance ion sources (ECRISs) are particularly useful for nuclear, atomic, and high energy physics, as unique high current generators of multicharged ion beams. Plasmas of gas discharges in an open magnetic trap heated by pulsed (100 micros and longer) high power (100 kW and higher) high-frequency (greater than 37.5 GHz) microwaves of gyrotrons is promising in the field of research in the development of electron cyclotron resonance sources for high charge state ion beams. Reaching high ion charge states requires a decrease in gas pressure in the magnetic trap, but this method leads to increases in time, in which the microwave discharge develops. The gas breakdown and microwave discharge duration becomes greater than or equal to the microwave pulse duration when the pressure is decreased. This makes reaching the critical plasma density initiate an electron cyclotron resonance (ECR) discharge during pulse of microwave gyrotron radiation with gas pressure lower than a certain threshold. In order to reduce losses of microwave power, it is necessary to shorten the time of development of the ECR discharge. For fast triggering of ECR discharge under low pressure in an ECRIS, we initially propose to fill the magnetic trap with the plasmas of auxiliary pulsed discharges in crossed ExB fields. The glow plasma trigger of ECR based on a Penning or magnetron discharge has made it possible not only to fill the trap with plasma with density of 10(12) cm(-3), required for a rapid increase in plasma density and finally for ECR discharge ignition, but also to initially heat the plasma electrons to T(e) approximately = 20 eV.

Microwave-assisted synthesis of La 1− xB xMnO 3.15 (B = Sr, Ag; x = 0 or 0.2) via manganese oxides susceptors and their activity in methane combustion

La 1− x B x MnO 3.15 perovskites (B = Sr, Ag; x = 0 or 0.2) were synthesised from metal nitrates in a short time (ca. 15 min) using microwave irradiation. The manganese oxides formed, after metal nitrates decomposition, are efficient microwave receptors and absorb energy strongly at 2450 MHz (microwave frequency). This absorption increased the microwave power loss in the material and led to local heating which provided the necessary energy for La 1− x B x MnO 3.15 formation. X-ray powder diffraction indicated the formation of crystalline La 1− x B x MnO 3.15 perovskites. The solids were also characterised by TPR and SEM techniques. The La 1− x B x MnO 3.15 perovskites were used as catalysts for catalytic combustion of methane. It was found that the catalytic activity of microwave-synthesised perovskites is better than that observed with the corresponding perovskites synthesised by conventional process. Finally, sintering of perovskites was carried out under microwave radiation and the catalytic behaviour of sintered catalysts is described.

Microwave nonlinear resonance incorporating the helium heating effect in superconducting microstrip resonators

Nonlinear microwave phenomena in superconducting niobium–teflon microstrip resonators cooled by liquid helium are studied. Helium heating caused by the losses of microwave power in superconductor changes the resonant frequency because of the temperature dependence of helium permittivity. Manifestations of this thermal instability discover a new type of nonlinear phenomena including the generation of the monochromatic microwave pulses, generation of acoustic signals. The found nonlinear resonances are explained by thermally induced variations of the helium dielectric permittivity caused by the microwave power dissipated in superconductor, which enable incorporating the jump nonlinearity of a liquid–vapour phase transition in helium.

Development of an intravascular heating source using an MR imaging guidewire.

To develop a novel endovascular heating source using a magnetic resonance (MR) imaging guidewire (MRIG) to deliver controlled microwave energy into the target vessel for thermal enhancement of vascular gene transfection. A 0.032-inch MRIG was connected to a 2.45-GHz microwave generator. We 1) calculated the microwave power loss along the MRIG, 2) simulated the power distribution around the MRIG, 3) measured the temperature increase vs. input power with the MRIG, and 4) evaluated the thermal effect on the balloon-compressed/microwave-heated aorta of six living rabbits. In addition, during balloon inflation, we also simultaneously generated high-resolution MR images of the aortic wall. The power loss was calculated to be 3.9 dB along the MRIG. The simulation-predicted power distribution pattern was cylindrically symmetric, analogous to the geometry of vessels. Under balloon compression, the vessel wall could be locally heated at 41 degrees C with no thermal damage apparent on histology. This study demonstrates the possibility of using the MRIG as a multifunctional device, not only as a receiver antenna to generate intravascular high-resolution MR images of atherosclerotic plaques and as a conventional guidewire to guide endovascular interventions during MR imaging, but also as a potential intravascular heating source to produce local heat for thermal enhancement of vascular gene transfection.

Microwave synthesis of magnetoresistive La0.7Ba0.3MnO3 using inorganic precursors

We report here the use of inorganic precursors as good microwave absorbers, by virtue of its polarity and high dielectric constant, to synthesize high temperature stable rare earth manganite, La0.7Ba0.3MnO3. Compared to other wet chemical methods, the oxides prepared by microwave assisted route give fine particle oxides (<30 nm) with effective BET surface area of ∼25 m2/g. Two factors contribute to the rapid synthesis of these high temperature phases. Firstly, the dielectric constant of the precursors employed increases the microwave power loss in the material and this leads to a local heating effect. Secondly decomposition of these precursors, lead to formation of finely divided oxides often accompanied by an exothermic reaction which provides the needed energy to effect the formation of the product. This method offers a new approach to employ inorganic precursors as starting materials to realize fast and effective reaction in microwave assisted material synthesis.

Effects of granularity on magnetic field dependent microwave response and surface degradation in thin films of YBa 2Cu 3O 7−δ

The magnetic field dependent microwave power loss in thin films of YBa 2Cu 3O 7−δ is analysed using the technique of non-resonant microwave absorption. The loss is correlated to the surface quality, specifically to the granularity of the film as determined by scanning electron microscopy and atomic force microscopy. We also observe that a granular surface is sensitive to degradation under aqueous attacks.

Effect of increasing hygroscopicity on the microwave heating of solid foods

The effect of a progressive increase in the bound strength of moisture in soybeans — a porous hygroscopic solid — during microwave heating is investigated. Thin layers of soybeans were dried with a single mode (TE 10) microwave cavity operating at 2450 MHz. The absorbed microwave power, temperature, and mass loss of the seeds were monitored continuously. Under a constant absorbed microwave power of 0.57 W/g, the temperature of a soybean seed increased rapidly at the initial stages of drying, reached a maximum of about 75 °C in approximately 50 min, and decreased gradually during the latter stages of drying to about 58 °C in 150 min. To maintain a constant drying temperature the absorbed microwave power had to be progressively increased as required. The results indicate that drying increases the average bound strength of the remaining moisture in a hygroscopic material and the energy needed to evaporate a unit mass of moisture increases accordingly. Consequently, progressively higher absorbed microwave powers are needed to maintain the temperature of low moisture solid foods during microwave heating processes that are accompanied by significant moisture loss.

Melt-textured YBa/sub 2/Cu/sub 3/O/sub 7/ for low-field applications in microwave devices

We report the results of an investigation of microwave power loss at 10 GHz in YBCO at 77 K. The samples are melt-textured YBa/sub 2/Cu/sub 3/O/sub 7/ (123) with 28 mole % Y/sub 2/BaCuO/sub 5/ (211) inclusions and x% of Ag added to bridge the gaps at the grain boundaries. The sample with 10% Ag shows critical currents >10/sup 8/ amp/m/sup 2/ at 77 K. Measurements down to 77 K show that microwave power loss drops more sharply (through T/sub c/ of 89 K) with higher Ag content. DC magnetic-field-induced microwave absorption (MWMA) recorded at 77 K shows that in these samples the low (/spl sim/10 mT) field loss is drastically reduced with respect to that in typical YBCO ceramics. >

Measurement of transition temperatures (simultaneously at DC and microwave frequencies) on high-Tc superconducting systems

A technique for the simultaneous measurement of the dc conductivity and microwave (ac) properties on the same sample is described. The difference in transition temperatures between dc and microwave frequencies (i) at ≈6.2 GHz (J-band), ≈9.2 GHz (X-band), ≈13.5 GHz (P-band), and ≈17.8 GHz (P-band) on YBaCu oxide and (ii) at ≈6.2 GHz on YBaCu oxide thin films and BiPbSrCaCu oxide has been evaluated. From the observations of these simultaneous measurements, the energy dependent variations of these simultaneous measurements, the energy dependent variation of ΔTc (Tc(dc) – Tc(ac)) and the non-zero microwave power loss beyond the superconducting transition temperature are discussed.

Comparison of the effect of processing parameters and degradation on the DC and microwave properties of thin films and polycrystalline bulk high-Tc superconducting materials

The sharp increase in microwave power loss (the reverse of what has previously been reported) at the transition temperature in high-Tc superconducting systems such as YBaCu oxide (polycrystalline bulk and thin films obtained by the laser ablation technique) and BiPbSrCaCu oxide is reported. The differences between DC resistivity ( rho ) and the microwave power loss (related to microwave surface resistance) are analysed from the data obtained by a simultaneous measurement set-up. The influence of various parameters, such as preparation conditions, thickness and aging of the sample and the probing frequency (6-18 GHz), on the variation of microwave power loss with temperature is outlined.